This invention relates to an apparatus that detects energization of high voltage lines (i.e., 2000 volts and higher) without direct connection (i.e., non-contact) to such lines. More particularly, this apparatus relates to an apparatus that detects the electric field (i.e., E-field) surrounding high voltage transmission and distribution lines used for electrical utility power distribution.
Electrical utilities need to monitor their power lines to determine when lines are down or in need of repair, and when power transmission to specific areas needs to be re-routed. Transmission lines route high voltage electrical power from power plants to main regional stations and local substations. Distribution lines route high voltage electrical power from substations to end users. In many areas such lines are above ground exposed to natural elements. Thus, high winds, falling trees or other forces occurring during storms or natural disasters may de-energize or "knock out" a line.
Some electrical utility companies employ Supervisory Controls and Data Acquisition (SCADA) systems with automatic sectionalizing procedures to sense the activities of their power lines and react automatically to line failures. Typically, substations have incoming and outgoing high voltage transmission lines which feed transformers that step down the voltage a lower voltage (i.e., 12 kV) for distribution to end user residences and businesses. Previously, when a power line is knocked down, a coupled voltage transformer (CVT) typically senses the loss of voltage. The CVT has a primary winding connected directly to the 115 kV line and a secondary winding driving a relay to a normally open position. When the line is knocked down, the signal across the primary winding is discontinued causing the signal on the secondary winding to discontinue. The loss of signal on the secondary winding closes the relay, starting a motor that opens switches on all de-energized 115 kV lines at the substation.
The electrical utility monitors the CVT signals via remote communication within the SCADA systems to determine which lines in a region are active. A failed power line is bypassed, when possible, and power re-routed through other lines. The CVT devices are expensive devices directly connected to power lines. The power lines need to be shut down, when possible, to install and replace such devices. Accordingly, there is a need for a non-intrusive monitoring device which monitors power lines and is linked to SCADA systems.
A non-intrusive way of detecting the presence of electrical signals is to detect the E-field surrounding the lines carrying the signal. There are E-field detectors known for detecting low voltage (i.e. 440 volts or less) activity. FIG. 1 shows one such low voltage sensor device manufactured by Radio Shack under the Micronta.RTM. trademark. The sensor device 10 includes a set of serially connected hex inverters 12 (MC 14069 UBCP) receiving an induced input signal 14. The sensor device 10 is activated by pressing switch 16. The switch passes a 3 V dc power signal to the inverters 12. When the switch 16 is depressed and an input signal above a minimum input sensitivity voltage is received, the input signal voltage is amplified to drive transistor 17 which in turn drives photodiode 18. When the input is above the minimum sensitivity the photodiode stays lit. The greater the input signal voltage, the brighter the photodiode 18 output up until a point at which the driving transistor 17 saturates. Voltage limiting circuitry including resistors 20, 22, 24, 26 and capacitor 28 protect the inverters 12 from voltage input signals above a specific value.
The prior art voltage sensor of FIG. 1 and other low voltage sensors over-saturate in the presence of high voltage signals (such as the approximately 2000 volts or higher contemplated by this invention). The sensor of FIG. 1 also has a poor response to voltage transients when over-saturated. Accordingly, there is a need for a non-contact apparatus which can detect the E-field of high voltage (i.e., 2000 volts or higher) signals without over-saturating and which can respond quickly enough to sense voltage transients.